Anyone affected that much by the weight of an HMD is probably too ill to sit up in bed.
A DK2 is heavy. It won't make your head fall off, but after you have been wearing it for a few hours, you will experience neck ache. At least until your neck gets used to it. I've clocked hundreds of hours on my DK2, so I am speaking from personal experience and I have no illness or medical condition. I'm in perfect health.
The first Vive was pretty much the same as the DK2 in terms of weight and the side of straps. I understand the release Vive is a little lighter, but not by much.
The other issue with the DK2 (and the Vive I tried) was the big warm screen and the large straps stop you losing heat through your head, quite the reverse - you get warmer. So while that's no a problem on cooler days, when the warm weather hits you have to stop playing. It is just too uncomfortably hot.
The primary reasons for my choosing the CV1 were that is was lighter, with smaller straps and used a breathable material. I don't think that will eliminate the DK2's problems totally, but it will greatly reduce them.